Typically, in a modern wireless communications system, a plurality of cells or NodeBs (NB) (also commonly referred to as base stations, base terminal stations, communications controllers, and so on) may be arranged into a cluster of cells, with each cell having multiple transmit antennas. Additionally, each cell or NB may be serving a number of users (also commonly referred to as User Equipment (UE), mobile stations, terminals, and so forth) based on a priority metric, such as fairness, proportional fairness, round robin, and so forth, over a period of time.
Usually, the NBs may be arranged close to each other so that a decision made by a first NB may have an impact on a second NB. For example, the NBs may use their transmit antenna arrays to form beams. This may mean that if the first NB decides to serve a first UE in a particular time-frequency slot, it may form a beam pointing to that UE. However, the pointed beam may extend into a coverage area of the second NB and cause interference to UEs served by the second NB. The inter-cell interference (ICI) for small cell wireless communications systems is commonly referred to as an interference limited cell scenario, which may be different from a noise limited cell scenario seen in large cell wireless communications systems.
The amount and type of interference that the first NB causes to UEs in the coverage area of the second NB may depend on which UE the first NB chooses to schedule in a particular time-frequency slot. Usually and until recently, each NB may independently make such scheduling decisions and let the UEs independently deal with the interference fluctuations.
In a commonly used solution, a NB may be used to apply a safety back off margin to a reported channel quality indicator (CQI) message from a UE to its serving NB. The NB may then use the backed off version of the CQI to perform link adaptation and select a modulation and coding selection (MCS) level thereon. Another commonly used solution may be for either the NB or the UE to average several measured CQIs in order to average out the CQI fluctuations. Alternatively, coordination between cells may be used to reduce the amount of interference.